Hydropneumatic piston accumulator

ABSTRACT

A hydropneumatic piston accumulator, with an accumulator housing ( 1 ), which comprises a cylindrical tube ( 3 ) defining a longitudinal axis ( 11 ), wherein the cylindrical tube ( 3 ) is closed at both ends by a housing cover ( 5, 7 ) at each end and wherein a piston ( 9 ) is longitudinally movable in the cylindrical tube ( 3 ) and, in the housing, separates a working chamber ( 13 ) for a compressible medium, such as a working gas, from a working chamber for an incompressible medium, such as hydraulic fluid, and with a displacement measuring device for determining the position of the piston ( 9 ) in the housing in a contact-free manner. The invention is characterised in that the displacement measuring device comprises a non-magnetic measuring tube ( 29 ), which extends along the longitudinal axis ( 11 ) from one housing cover ( 5 ) to the other housing cover ( 7 ) through a passage ( 31 ) formed in the piston ( 9 ) and is sealed against the interior of the housing ( 1 ), and in that in the tube ( 29 ) a position sensor ( 57 ) is movably guided and follows the piston movements in the measuring tube ( 29 ) using a magnetic force acting between the piston sensor ( 57 ) and the piston ( 9 ), and in that a transmitter/receiver ( 65 ) for the displacement measuring device is positioned on one of the housing covers ( 5, 7 ) and emits a measurement beam through the open end ( 25, 26 ) of the measuring tube ( 29 ) to the position sensor ( 57 ) and receives reflected radiation from same.

The invention relates to a hydropneumatic piston accumulator, comprising a storage housing having a cylinder tube defining a longitudinal axis, which is closed at both ends by a relevant housing cover and in which a piston can be moved longitudinally, which piston separates a working chamber for a compressible medium, such as a working gas, from a working chamber for an incompressible medium, such as hydraulic oil, in the housing and having a displacement-measuring device for determining the position of the piston in the housing in a non-contacting manner.

Hydraulic accumulators, such as hydropneumatic piston accumulators, are used in hydraulic systems to receive and return certain volumes of pressurized fluid, such as hydraulic oil, to the system as needed. In today's conventional hydropneumatic piston accumulators, in which the piston separates the oil-side working chamber from the working chamber receiving a working gas such as N₂, the position of the piston changes such that the accumulator absorbs hydraulic oil as the pressure increases, thereby compressing the gas in the other working chamber. With decreasing pressure, the compressed gas expands, displacing stored hydraulic oil back into the hydraulic circuit. The resulting changes in the volumes of the work chambers in operation causes a corresponding axial movement of the piston in every case.

A prerequisite for the desired flawless performance of the storage is the adaptation of the pressure in the working chamber of the working gas to the pressure level in the oil-side working chamber, such that the piston is positioned at appropriate locations within the storage housing to perform the working movements between piston end positions in the storage housing. The determination of the position the piston occupies at a given fluid pressure in the oil-side working chamber also provides information on the amount of the filling pressure of the working gas in the assigned working chamber and thus the monitoring of the piston accumulator for proper functioning.

Various solutions to determine the position of the piston have been proposed. From document DE 10 2013 009 614 A1, for example, an ultrasonic displacement measuring system is known, in which, starting from the housing cover adjacent to the working chamber containing the working gas, an ultrasonic sensor is used to determine the distance to the facing side of the piston. This solution is rather elaborate because a continuous error correction of the result obtained by a running time measurement has to be performed due to the changing sound propagation velocity in the working chamber containing the gas. In a further known solution, which is disclosed in DE 103 10 427 A1, a row of magnetic field sensors is arranged on the outside of the storage housing, which respond to the field of a magnet arrangement, which is located on the piston of the piston accumulator. This solution leaves much to be desired in that a magnetic strip containing the magnetic sensors has to be attached to the storage housing as an exterior component.

Based on this prior art, the invention addresses the problem of providing a hydropneumatic piston accumulator of the type mentioned, the displacement-measuring device of which permits the determination of the position of the piston in a particularly simple and advantageous manner.

According to the invention, this object is achieved by a piston accumulator having the features of claim 1 in its entirety.

According to the characterizing part of claim 1, the displacement-measuring device according to the invention has a non-magnetic measuring tube, which extends through a passage formed in the piston along the longitudinal axis of a housing cover to the other housing cover and is sealed against the interior of the housing. A position sensor used for measuring, which is displaceably guided in the measuring tube, follows the movements of the piston upon the action of a magnetic force acting between piston and position sensor in the measuring tube. A transmitter/receiver of the displacement-measuring device located on a housing cover sends a measuring radiation to the position sensor through the relevant open end of the measuring tube and receives the reflected radiation therefrom. Because the interior of the measuring tube forms a measuring zone independent of the physical state of the interior of the housing, a chamber with constant media pressure and constant media density is available for the passage of the measuring radiation, such as ultrasound. Thus, at a constant speed of sound, a distance measurement by means of a displacement-measuring device having an ultrasonic transmitter/receiver can be performed easily and accurately without measures for error correction being required. It goes without saying that the measuring tube can also be used to conduct a laser measurement.

To generate the magnetic force forcing the subsequent movements of the position sensor in the measuring tube, a permanent-magnet device may advantageously be provided on the piston, which device entrains the position sensor during the travel of the piston, which transmitter is formed of a ferromagnetic material or is provided with ferromagnetic components.

For the generation of a particularly high force of attraction acting on the position sensor, a permanent-magnet device can also be provided on the position sensor, for example a magnetically hard ferrite core located in the position transmitter.

In a particularly advantageous manner, the permanent-magnet device on the piston can have a magnetic ring mounted to the passage of the piston surrounding the measuring tube.

In particularly advantageous embodiments, in which the position sensor has two circular disks extending on a plane radial to the longitudinal axis, which disks are interconnected by a coaxial, radially inwardly offset connecting part, the axial spacing of the flat end surfaces of the disks preferably corresponds to the axial height of the magnetic ring on the piston. In the case of an axial polarity of the magnetic ring, a high magnetic flux density and a high magnetic force effect, forcing the safe subsequent movement of the position sensor, result at the disks of the position sensor.

Advantageously a ferrite core, which is polarized in the axial direction reversed to the magnet ring, can be provided in the connecting part of the disks as a permanent-magnet device on the position sensor.

For a magnetic decoupling of the magnetic ring relative to the piston material, in advantageous exemplary embodiments the magnetic ring is connected to the piston via an intermediate body made of non-magnetic material. It may be formed from a thermosetting plastic and mounted onto the piston by screws, which are preferably also non-magnetic.

Advantageously, the arrangement can be made such that one end of the measuring tube is firmly connected to a housing cover, for example by means of a soldered or welded connection, and the other end engages with a passage located on the other housing cover, leading towards the outside, in which the open end of the tube is sealed against the interior of the housing and a seat is formed for the displacement-measuring device.

In doing so, the seat in the housing cover in question can receive the transmitter/receiver for sending and receiving an optical or preferably ultrasound-acoustic measuring radiation passing through the open end of the measuring tube.

The seat for the displacement-measuring device may be provided on the housing cover adjacent to the oil-side working chamber. Advantageously, in this way the port connections of the displacement-measuring device and the pipe leading to the assigned hydraulic system, which is connected to a port opening, which is located in this housing cover, are located on one and the same side of the storage housing.

On the housing cover, which is opposite the housing cover having the seat of the displacement-measuring device, the measuring tube may be connected to the environment. The pressure-resistant measuring tube is thus pressureless, i.e. no particularly elaborate sealing is required at the passage, which forms the seat for the displacement-measuring device. For an unpressurized measuring tube, the displacement-measuring device can also be removed from the piston accumulator after the measuring periods have been completed without interrupting the latter's operation.

Below the invention is explained in detail with reference to exemplary embodiments shown in the drawing.

In the drawings:

FIG. 1 shows a shortened longitudinal section of an exemplary embodiment of the piston accumulator according to the invention; and

FIG. 2 shows a likewise shortened longitudinal section of a second exemplary embodiment.

The piston accumulator according to the invention has a storage housing designated as a whole by 1, which housing has a cylinder tube 3 forming a round hollow cylinder shown as the main part in both exemplary embodiments. It is sealed at both ends by a screwed housing cover 5 and 7, respectively, between which a piston 9 is freely movable along the longitudinal axis 11 of the housing. The piston 9 separates a gas-side working chamber 13, which receives, a working gas, such as nitrogen, which is pressurized with a filling pressure, as a compressible medium, from a working chamber 15, which receives an incompressible medium, such as hydraulic oil. For the connection of this working chamber 15 to an assigned hydraulic system, which is not shown, a port opening 16 is provided in the housing cover 7 adjacent to the oil-side working chamber, which is arranged in the area between the longitudinal axis 11 and the radially outer end of the housing cover 7. On the opposite housing cover 5, which is adjacent to the gas-side working chamber 13, also offset from the longitudinal axis 11, a filling channel 17 is provided at the outer end of which a filling valve 21 of the usual type is arranged, which can be used to introduce the fill quantity of working gas pressurized at filling pressure into the working chamber 13. In coaxial arrangement to the longitudinal axis 11, a passage opening 27 is formed in this housing cover 5 adjacent to the gas-side working chamber 13. It has the form of a stepped drilled hole with an inner, enlarged section of the drilled hole 23, which forms a suitable seat for the inserted, open end 25 of a measuring tube 29, in which the open end 25 of the measuring tube 29 is sealed against the adjacent working chamber 13. The opposite end 26 of the measuring tube 29 engages with a coaxial through-hole 28 in the housing cover 7 adjacent to the oil-side working chamber 15. Similar to the through hole 27, the drilled hole 28 is stepped at the other housing cover 5, wherein the end 26 of the measuring tube 29 is mounted in a section of a drilled hole, where the sealing elements 19 and 20 seal the pipe end 26 against the working chamber 15. The end 25, which is seated in the drilled-hole section 23 of the housing cover 5 adjacent to the gas-side working chamber 13 of the measuring tube 29, which is formed of a pressure-resistant, non-magnetic metallic material, is attached to the housing cover by means of a soldering or welding connection 24. The measuring tube 29 may extend into the interior of the storage housing over its entire length; however, in particular at the lower end of the measuring tube 29, can also end in a pressure-tight manner, while maintaining an axial distance from the housing cover 5.

A central passage 31 is formed for the measuring tube 29 in the piston 9. Otherwise, the piston 9 is formed in the usual manner for such accumulator pistons and has recessed annular grooves 33 and 35 on its outer circumference for piston seals, not shown, and, offset from these towards the two axial end areas, flatter annular grooves 37 and 39 for guide rails, also not shown. As is also customary in such pistons, the piston 9 has a round cup-shaped recess 41, the flat bottom 43 of which is located at approximately half the axial length of the piston 9, on the piston side, which faces the gas-side working chamber 13 in the storage housing 1. The bushing 31 has a through hole 51, which extends coaxially to the longitudinal axis 11, starting from the bottom 43 to the piston end side. In the area of the drilled hole adjoining the bottom 43, the drilled hole has a circular cylindrical extension 53, which forms the seat for an annular body 45, which is mounted in the extension 53 by screws 47 running in parallel to the drilled hole 51. Ring grooves 49 and 50 are formed in the non-expanded part of the drilled hole 51 for sealing rings.

The annular body 45 mounted in the extension 53 forms the support for a permanent-magnet device, which generates a magnetic force, the attraction force of which acting on a position sensor 57 displaceable in the measuring tube 29 forces the position sensor 57 to follow the movement of the piston 9 in the measuring tube 29. In the exemplary embodiments shown, the permanent-magnet device of the piston 9 is formed by a magnetic ring 55, which is mounted by gluing to a free surface of the annular body 45 flush with the bottom 43. The screws 47 and the annular body 45 are made of thermosetting plastic to magnetically decouple the magnetic ring 55 from the metallic piston 9.

In the embodiment of FIG. 1, the position sensor 57 is formed as an integral round body of a ferromagnetic material, which has a flat circular disk 58 at both axially opposite ends, on the outer diameter of which the position sensor 57 is displaceably guided in the measuring tube 29. The disks 58 are integrally connected to one another via a reduced-diameter connecting part 59. The axial distance of the disks 58 is adapted to the axial height of the magnetic ring 55 such that the end surfaces of the disks 58 are aligned with the axial end surfaces of the magnetic ring 55, such that an optimal magnetic flux is formed with the magnetic ring 55. The end face of the disk 58 of the position sensor 57, which faces the end 26 of the measuring tube 29, forms the reflection surface for the measuring radiation entering the measuring tube 29 from the end 26.

The stepped drilled hole 28 of the housing cover 7 receiving the end 26 of the measuring tube 29 has on the passage 31 of the piston 9, similar to the drilled hole 51, a circular cylindrical extension 54, in which the same annular body 45, as is also used on the passage 31 of the piston 9 as a plastic body, is mounted and secured using screws 47. The annular body 45 forms a suitable apron of the inserted end section of the measuring tube 29 on the housing cover 7. The displacement-measuring device has a transmitter/receiver 65 for an ultrasonic measuring process, for which the outer, extended section of the drilled hole 67 of the drilled hole 28 forms a seat in the oil-side housing cover 7. Starting from this section of the drilled hole 67, an ultrasonic transducer with a disk-shaped piezoceramic 68 extends into the end area of the tube 29 to perform the determination of the distance from the reflection surface on the facing disk 58 of the position sensor 57.

The exemplary embodiment of FIG. 2 differs from FIG. 1 only insofar as a hard magnetic ferrite rod 71, instead of the connecting part 59 integral with the disks 58 of the position sensor 57, is inserted as a connecting part between the disks 58. This is oriented such that its polarity is opposite the axial polarity of the magnetic ring 55, such that a strong magnetic force effect results and thus a particularly safe tracking of the position sensor 57 is ensured in the travel movements of the piston 9.

It goes without saying that, instead of the ultrasonic measuring method, different types of measuring radiation can be used, for example using laser light or monochromatic visible light by means of optical methods. In the case of a measuring zone enclosed in the measuring tube 29, isolated from the interior of the housing, the measuring operation can be performed from an arbitrarily selected end 25 or 26 of the measuring tube 29. In contrast to the figures, the transmitter/receiver 65 can also be arranged on the gas-side housing cover 5, wherein the extended, end-side drilled hole section 73 of the through hole 27 could form the seat for the displacement-measuring device. 

1. A hydropneumatic piston accumulator, having a storage housing (1) comprising a cylinder tube (3) defining a longitudinal axis (11), which is closed at both ends by one housing cover (5, 7) each and in which a piston (9) can be moved longitudinally, which separates a working chamber (13) for a compressible medium, such as a working gas, from a working chamber for an incompressible medium, such as hydraulic oil, in the housing, and having a displacement-measuring device for determining the position of the piston (9) in the housing in a non-contacting manner, characterized in that the displacement-measuring device comprises a non-magnetic measuring tube (29), which extends along the longitudinal axis (11) from a housing cover (5) to the other housing cover (7) through a passage (31) formed in the piston (9) and which is sealed towards the interior of the housing (1), in that a position sensor (57) is displaceably guided in the tube (29) to follow the piston, movements due to magnetic force acting between the sensor and the piston (9) in the measuring tube (29), and in that a transmitter/receiver (65) of the displacement-measuring device is arranged in one of the housing covers (5, 7), which emits the measuring radiation passing through the relevant open end (25, 26) of the measuring tube (29) to the position sensor (57) and receives any radiation reflected by the latter.
 2. The piston accumulator according to claim 1, characterized in that a permanent magnet means (55) is provided on the piston (9) for generating the magnetic force forcing the subsequent movements of the position sensor (57) in the measuring tube (29).
 3. The piston accumulator according to claim 1, characterized in that a permanent magnet means (71) for generating the magnetic force forcing the subsequent movements of the position sensor (57) in the measuring tube (29) is also provided on the position sensor (57).
 4. The piston accumulator according to claim 1, characterized in that the permanent magnet means on the piston (9) has a magnetic ring (55) surrounding the measuring tube (29) and mounted at the passage (31) of the piston (9).
 5. The piston accumulator according to claim 1, characterized in that the position sensor (57) has two circular disks (58) extending in a plane radial to the longitudinal axis (11), which are interconnected by a coaxial, radially inward offset connecting part (59) such that the axial distance of the flat end surfaces of the disks (58) corresponds to the axial height of the magnetic ring (55) on the piston (9).
 6. The piston accumulator according to claim 1, characterized in that the magnetic ring (55) is connected to the piston (9) via an intermediate body (45) consisting of a non-magnetic material.
 7. The piston accumulator according to claim 1, characterized in that on one end (25) the measuring tube (29) is firmly connected to a housing cover (5) and the other end (26) engages with an outward passage (28), located in the other housing cover (7), in which the open end (26) of the tube (29) is sealed against the housing interior and a seat (67) is formed for the displacement-measuring device.
 8. The piston accumulator according to claim 1, characterized in that the transmitter/receiver (65) for sending and receiving optical or preferably acoustic measuring radiation passing through the open end (26) of the measuring tube (29) is mounted to the seat (67) of the relevant housing cover (7).
 9. The piston accumulator according to claim 1, characterized in that the seat (67) for the displacement-measuring device is provided on the housing cover (7) adjacent to the oil-side working chamber (15).
 10. The piston accumulator according to claim 1, characterized in that the measuring tube (29) on the housing cover (5), which is opposite the housing cover (7) having the seat (67) of the displacement-measuring device, is connected to the environment. 